Find The Accelerations A₁, A₂, A, Of The Three Blocks Shown In Figure, If A 1 Horizontal Force Of 10 N Is Applied On (A) 2 Kg Block, (B) 3 Kg Block, (C) 7 Kg Block. Take G = 10 M/S².

[Gauravohcphcphcp]

Find the accelerations a₁, a₂, a, of the three blocks shown in figure, if a 1 horizontal force of 10 N is applied on (a) 2 kg block, (b) 3 kg block, (c) 7 kg block. Take g = 10 m/s².

[bhg481]

The problem with asking people to do your homework for you is that they can't help without the diagram.

[Dizmo]

Does it (the diagram) look anything like this? https://i.lowrex.com/i/Be8wF.png

[bobbinwales]

done this stuff at night school in the 80s
We had to learn alot of tech formulas like friction is F = μR (horizontaly) and F =mg.... stick in your mind forever/
R is the verticle weights in your Q so m x g. and your μs are shown in your diagram if its the same as dizmos, but use whatever yours shows.
I wont spoil the rest for you (Ok hands up I can't do it all them year's later, never was top student, but you'll have some examples in your books???)

[bobbinwales]

Please give us your answer and working when you get it....would be intrested to see if I still get it

[Peter Pedant]

bobbs is correct
there is more than one U-tube program on this



apply as necessary - which has been the subject of your own lessons. This is formulaic, everyone does this in an A level course. I did in 1968. You just sit thro them and apply them to your own prob.

[Peter Pedant]

oops sozza I thought they were triangular

[bobbinwales]

Will watch the clip later but thats abit more advanced with slopes, angles and all that trig stuff I've forgot

[bobbinwales]

typed mine while you were posting Peter- not sure what triangular means here but maybe your saying about the angles

[Peter Pedant]

stacked blocks are here
(c) is easy 17k and no friction
apply F = ma 10= 17 a.

For b and a you have to decide if c the third block moves or not
I will have to watch the video

[bobbinwales]

found this,,,, abit long but I might watch when Corrination St gets too silly

[Peter Pedant]

yeah we did traingular block frictionlessly sliding down each other. Trick is to remember that the acceleration is a vector

( thx to Fatty Barrett)

[Peter Pedant]

I cant believe that the poster asked a question like this when he has had a lesson on it - perhaps he slept thro it
and if he sleeps thro the videos , then he STILL wont be able to do it !

[ZebuSanctuary]

Gaura, Are you still with us?

We cannot help you if you don't provide the coefficients of friction. Diagram would be handy but not essential.

[kuiperbelt]

I will attempt to work out 2 BLOCK STACK which hopefully will be of help to Gauravohphcphcp.


FN1 FN2
| |
| |
| |
---------------------- ------------
F = 10 N | | Fr | |
---------->| 7kg | Fr = 0.3 x 3 x 10 -> Fr = 9 N but also Fr ` = m x a therefore 9N = 3kg x a
So max acceleration before 3kg block slips is 3 m/s^2
This translates to a Max Force (before slippage) of 10kg (7kg + 3kg) x 3m/s^2 = 30 Newtons.

So with 10 N applied we know 3kg block will not slip.
F + Fr = ma -> (10 + 9)/7 = a --- BODMAS --- 19/7 acceleration with 10N applied ---- Answer 2.7 m/s^2

[kuiperbelt]

Oh know my sketch of the problem failed to come out properly.

[ZebuSanctuary]

Kuiper, The first part is correct and complies with the general formula for a 2 block stack where the bottom block (7kg) is on a frictionless surface i.e., there is no static friction hence µ = 0.

General formula for maximum force F on frictionless surface;

F = µ m2 g (1 + m1/m2) Newtons

Where static friction µ = 0.3, m2 = 3kg , m1 = 7kg and g = 10m/s²

Thus 0.3 x 3kg x 10m/s² (1 + 7kg/3kg) = 30 N

This leads to maximum acceleration before slippage occurs of 3 m/s² as you have correctly calculated.

Where you have gone wrong is to assume the Frictional Force (horizontal vector) is acting Left to Right. The problem is rather intuitive and upon reassessing you’ll see the horizontal vector must be acting from Left to Right. NB: It will alternate in direction as you go up the stack.

One further amendment that is required, not to assume your Frictional Force (correct in the first part) is of the same amplitude for the second part of the question.

Hope this helps.

[kuiperbelt]

zebu/Hope this helps./

Problem is beyond me. In my opinion it is more advanced than A-Level physics.

[Dizmo]

I though my diagram was accurate. I guess not.

[kuiperbelt]

/I though my diagram was accurate/

Diagram good. Can you give me a pointer.

[Dizmo]

I wish I could. I've never been good at Math or Science (my English isn't great either).

I got the diagram from the exam/test paper :)